Pressure vessels have thick steel walls and so require very large forces to grow cracks. There is a number of different ways of investigating crack propagation in pressure vessel steels, one being to pull on a flat plate of the material using hydraulic equipment. Another involves pneumatically or hydraulically testing a pressure vessel made of the required material but in a scaled-down form compared with the size of pressure vessel for which a typical application of the steel in question, for example, the pressure vessel of a PWR Nuclear Reactor for power generation, can be considered. Each of the foregoing methods has some disadvantages.
Another alternative is axial rotation of a hollow cylinder made of the material in question at a speed sufficient to induce a hoop stress approaching the yield strength of the material, and it is with this method that equipment according to the invention is concerned.